As one of semiconductor manufacturing processes, there is a film forming process for forming a specific film on a surface of a semiconductor wafer (hereinafter, referred to as a “wafer”) W. In the film forming process, a material gas produced by vaporizing a liquid material is introduced as a film forming gas into an apparatus.
As examples of the film forming process using the material gas produced by vaporizing the liquid material, there are a case in which a SiO2 film is formed by using a processing gas obtained by vaporizing tetra ethyl oxysilane (TEOS) and oxygen (O2) gas, and a case in which a silicon nitride (Si3N4) film is formed by using a processing gas obtained by vaporizing Si2Cl6 and ammonia (NH3) gas.
A conventional example of a vaporizer for vaporizing the liquid material is illustrated in FIG. 5. The vaporizer of FIG. 5 includes a vertical cylindrical body 100 that is configured as a vaporization chamber and has a nozzle 101 installed at an upper portion thereof. At a leading end portion of the nozzle 101, a liquid material and a carrier gas are mixed to be discharged in a mist state into the cylindrical body 100 as in a sprayer. By heating the inside of the cylindrical body 100, the mist is vaporized to produce a gas material.
Meanwhile, recently, a liquid material having a low vapor pressure may be used due to the development of various devices. For example, a compound of hafnium (Hf) is employed as a film forming material.
For instance, Tetrakis(N-Ethyl-N-Methylamino)Hafnium (TEMAH) has a vapor pressure of about 0.11 kPa (0.85 Torr) at a temperature of about 85° C., and Hafnium Tetra-t-Butoxide (HTB) has a vapor pressure of about 0.55 kPa (4.12 Torr) at a temperature of about 85° C. These hafnium-based materials have a rather low vapor pressure, while TEOS has a vapor pressure of about 5.6 kPa (42 Torr) at a temperature of about 85° C.
The material having a low vapor pressure is difficult to be vaporized. For example, when the mist is adhered to an inner wall of the cylindrical body 100, the mist is dried and solidified at the inner wall and, then, detached from the inner wall to generate particles.
Meanwhile, when a heating temperature is raised to quickly vaporize the mist, it is difficult to uniformly heat the inside of the cylindrical body 100, and the mist may be decomposed and transformed by heating. Further, this phenomenon is more problematic when it is intended to increase a supply flow rate of the liquid material. As described above, it is very difficult to vaporize a low vapor pressure material, which is a problem to be solved in a film forming process using a new material.
In this connection, Patent Document 1 discloses a technique for improving vaporization efficiency by supplying a gas-liquid mixed fluid to a vaporizer and developing a structure of a nozzle to obtain a large amount of the gas material. However, a technique for increasing a flow rate of the gas material is still required.
Patent Document 1: Japanese Patent Laid-open Publication No. 2006-100737 (paragraphs [0023] to [0026])